A spiral type membrane filtering device (hereinafter simply referred to as the “membrane filtering device” is known that is constructed by plurally arranging the aforesaid spiral type membrane element (hereinafter simply referred to as the “membrane element”) in a line and connecting between the central pipes of adjacent membrane elements with use of an interconnector (connecting section). The plurality of membrane elements that are connected in this manner are housed, for example, in an outer vessel formed of resin, and are treated as one membrane filtering device (for example, refer to Patent Document 1).
A membrane filtering device of this kind is generally used for obtaining purified permeated water (permeated liquid) by filtering raw water (raw liquid) such as waste water or sea water. Particularly, in a large-scale plant or the like, numerous membrane filtering devices are held by a rack referred to as a train. For example, in a large-scale plant in which about 10000 tons of raw water are processed per day, 1000 or more membrane filtering devices are used.    Patent Document 1: Japanese Unexamined Patent Publication No. 2007-527318